Ventral Tegmental Area and Addiction

[gmanyo]

I was wondering how the ventral tegmental area (VGT) related to drug addiction and withdrawal. I was reading this topic on someone having no withdrawals from 5 years of opioid usage and I decided to research the mechanisms of opioid addiction and withdrawal and discovered that they're confusing as fuck.

I got to a couple interesting but confusing studies:
http://www.ncbi.nlm.nih.gov/pubmed/11264674
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2913611/?tool=pmcentrez

 

[Deleted member 170540]

Ventral tegmental area contains dopaminergic neurons that project to nucleus accumbens via the so called mesolimbic dopamine pathway. This is the 'reward pathway' of the brain. If electrodes are planted in the VTA of a lab animals brain and the animal is given the possibility to electrically stimulate its own VTA by pressing a lever, it will continue lever-pressing indefinitely.

Opioids act by hyperpolarizing GABAergic cells in the VTA and therefore reducing the inhibition of the dopaminergic cells that project to NAcc (GABA is an inhibitory neurotransmitter). This increases the dopamine input to NAcc and causes euphoria.

Repeated opioid self-administration causes neuronal changes in the VTA and results in a transition from recreational use to a chronically addicted state and compulsive use.

Most other drugs behave similarly, increasing dopamine input to NAcc by some mechanism.

The opioid withdrawal syndrome involves several neuronal mechanisms. For instance the noradrenergic locus coeruleus is overactivated in opioid or alcohol withdrawal, causing anxiety and peripheral sympathomimetic symptoms.